After a moderately quiet start once the NFL's free agency negotiating window opened Monday afternoon, things ramped up quickly Tuesday. The market, which doesn't officially open until 4 p.m. ET Wednesday, has already taken shape at key positions like quarterback, wide receiver and offensive line. Early agreements will likely set up subsequent waves of transactions that will follow throughout the week.

But here’s a look at how things have started to shake out:

Quarterback dominoes begin to fall

The first major move became apparent very early Tuesday morning, when the Denver Broncos and Case Keenum agreed to a contract that will reportedly pay him between $18-$20 million annually. For Denver, that represents a significant savings considering the price tag on Kirk Cousins will likely top out around the $28-$30 million range.

But the move also makes a lot of sense for Keenum, who earned a big payday after taking the Viking to the NFC title game. He gives the team a quality veteran with real grit and the ability to make big-time plays with targets like Demaryius Thomas and Emmanuel Sanders.

The Broncos liked Cousins. Their players lobbied publicly for him. Management appreciated his talent but did have some reservations when considering Cousins’ average numbers in the red zone and spotty performances in late-game situations. People familiar with the deliberations, who requested anonymity because of the sensitivity of the situation, told USA TODAY Sports that Broncos brass didn’t see a great level of separation between Keenum and Cousins and consequently opted for the more affordable option.

Keenum is an immediate upgrade over Trevor Siemian, Brock Osweiler and Paxton Lynch. At the very least, Keenum is a quality bridge for the next year or two given general manager John Elway might draft another passer with the fifth overall pick.

Elsewhere, the New Orleans Saints did the expected, hammering out a two-year deal to keep Drew Brees in black and gold. Monday featured some buzz that the Vikings had inquired about Brees’ services. But that nugget of information did little more than potentially serve as a bit of leverage for Brees in his negotiations.

With Minnesota apparently in the lead for Cousins, and the Cardinals opting for Sam Bradford, the Jets may have to settle for a consolation prize. That could mean AJ McCarron, Teddy Bridgewater or even bringing back Josh McCown as GM Mike Maccagnan likely turns to the draft. The Bills also must find an answer, whether that entails signing a free agent or continuing their quest to move up in the draft to select one of the top rookies. (And they could do both).

Receiver market dries up quickly

This wasn’t regarded as one of the best years for teams in need of wide receiver help because of a lack of game-changing talent in the draft and limited options in free agency.

That was a big reason why the Browns felt compelled to trade for Jarvis Landry, whom the Dolphins had designated as their franchise player. It's also why the Chiefs forked over a three-year deal that will pay Sammy Watkins roughly $16 million per season. That's quite a chunk of change for a wideout who, while earning $5.6 million last season, recorded just 39 catches for 593 yards and eight touchdowns.

Watkins advocates argue that he’s better than last season’s numbers suggest. He was traded from Buffalo to the Rams in early August and had to play catch-up for much of the year. But Watkins, the fourth pick of the 2014 draft, has just one 1,000-yard receiving campaign to his credit. While he is a red zone threat, his 25 TD grabs since he entered the league ranks behind other wideouts from his draft class: Odell Beckham (38), Mike Evans (32), Brandin Cooks (27) and Davante Adams (26). Still, it was obviously important to the Chiefs to give new starting quarterback Patrick Mahomes another weapon to go with Tyreek Hill, Kareem Hunt and Travis Kelce.

Meanwhile, the Bears are set to pay Allen Robinson $42 million over three years, according to multiple reports. The former Jaguar missed all but one game last season with a torn ACL but still found a lucrative pact and the chance to prove himself while potentially setting up an even bigger deal before he turns 28.

With Watkins and Robinson quickly snapped up, Washington promptly agreed to a five-year, $40 million contract with speedster Paul Richardson, who provides the Redskins an element they desperately wanted to pair with Josh Doctson and slot receiver Jamison Crowder.

Moving forward it will be noteworthy how Watkins' contract impacts Beckham, who's entering the final year of his rookie deal. OBJ wants to become the highest-paid receiver in the league, which means exceeding the $17 million annual average that Antonio Brown draws from the Steelers. Suddenly, perhaps Beckham isn't crazy to believe he deserves (mid-tier) quarterback money.

Guards get paid, too

The Jacksonville Jaguars opted against franchising Robinson. Instead, they chose to spend big on Panthers guard Andrew Norwell, who is expected to sign a five-year deal worth $66.5 million, including $30 million guaranteed, according to multiple reports. With that average salary of $13.3 million, he will become the highest-paid guard in the league.

It’s staggering that a guard is getting left tackle money. But Norwell can thank Oakland's Kelechi Osemele and Cleveland's Kevin Zeitler, who reset the bar for guards at $12 million per season a year ago.

Even coming off an all-pro effort, the Panthers were never prepared to break the bank for Norwell. But Jacksonville was surprisingly willing to ante up. It's clear that the Jags — they'd already hitched the wagon to inconsistent quarterback Blake Bortles earlier this offseason — felt beefing up the line was crucial to their success while ensuring the quarterback continues to develop and a top-ranked rushing attack continues to thrive.